In yet another advance since University of Hawai'i professor Ryuzo Yanagimachi cloned three generations of mice six years ago to establish the United States firmly as a player in cloning circles, the UH team, working with scientists in Japan, has now cloned an infertile male mouse.

The offspring also are infertile and carry no sperm-forming cells  just like the parent.

Yanagimachi said the development could help find solutions to infertility in humans.

"We can produce many infertile animals and use the animals to study the mechanisms of infertility," said Yanagimachi. "Right now if a man has no sperm-forming cell there's no way to cure infertility, but this is a step forward."

The new research produced in tandem by the UH Institute for Biogenesis Research and scientists at Kobe University, was published Tuesday in the Proceedings of the National Academy of Sciences.

Yanagimachi, a professor of anatomy and reproductive biology, first cloned a mouse  named Cumulina  in 1998, 15 months after the cloning in Scotland of Dolly the sheep. In its dramatic scientific advance, the UH lab produced additional generations of mice from the first clone, the first researchers to successfully replicate their work.

In non-scientific terms, a clone is an exact genetic duplicate of its forebear  with replication accomplished without sperm and by using genetic material from a single cell in the parent's body.

In this latest development, Yanagimachi worked with Teruhiko Wakayama, the same scientist he worked with at UH in 1998 when the Hawai'i team made its first breakthrough.

"The Honolulu Technique," as the Hawai'i method has been called, created more than 50 identical mice over three generations from a single cell.

In this new work, Yanagimachi helped Wakayama design the experiment and the Japan-based scientist did most of the work in carrying it out.

One of the additional authors of the paper is Wakayama's wife, Sayaka Wakayama.